As with most things electronic, there is a desire to continually make computers smaller and smaller, or in other words, to put the same or a greater amount of computing power within a given amount of space. As a part of this process, rack mounting designs were developed.
Rack mount systems provide a frame—also known as the rack—that has a standard width, such as nineteen inches or twenty-three inches, and a depth of no more than about thirty-two inches. Screw holes are provided down the height of the rack on either side of the standard width, to receive different rack-mount components. These components are typically specified as being 1 U, 2 U, 3 U, 4 U, and so-forth in height, where the term 1 U is used to define one rack unit of height. 1 U typically equals about 1.75 inches of rack height. Therefore, a 2 U component is about 3.5 inches high, a 3 U component is about 5.25 inches high, and a 4 U component is about seven inches high.
One component that can fit a rack mount system is a blade system. Blade designs put some aspects of a computer on a card (referred to as a blade) that is inserted into an enclosure (referred to as a chassis). Typically, the chassis is designed to accommodate several blades, such as four, eight, nine, sixteen, etc. The chassis typically provides elements of the system that can be commonly used for all of the blades in the system, which elements might be unnecessarily redundant if these elements were individually provided by each of the blades.
For example, power supply, cooling, and network or bus communications are typically provided by the chassis. These services might be provided in a redundant manner, but are provided in a manner that reliability and uptime are enhanced without unnecessarily providing duplicated services. The blade portion of the design is removable from the chassis and can be replaced or augmented, typically without powering down or otherwise taking the other blades off-line.
Blade systems are typically constructed with the blades fitting into the chassis in a vertical alignment, where the blades make electrical contact to the services provided by the chassis using a backplane connector, where the electrical connections are made by pushing the blade firming into the backplane at the rear of the chassis, and then the electrical connections are broken by pulling the blade even slightly out of the backplane connector. Thus, while one blade can be removed without powering down an adjacent blade, all of the components on a single blade must be powered down in order to even so much as physically inspect any of the components on that blade.
The blade computing design can be applied to different aspects of a computing system. For example, computers themselves can be configured into a blade design, where each blade in the system provides computing power with memory and a central processing unit. The blade concept can also be applied to data storage, with devices called storage blades or, alternately, drive blades.
Storage blades typically hold some number of individual hard drives, such as two, four, seven, eight, etc. However, it is always desirable for a storage blade system to hold as many drives as possible. The problem is that the number of drives is limited not only be the size of the rack in which the chassis is mounted, but also by the multiple of the unit depth, as described above, which might not align well with the actual height of the drives. Further, the material from which the blades are constructed can only take so much weight. Thus, there are constraints on the number of hard drives that can fit into a drive blade system. Further, the limitations of the blade concept tend to require that all of the components on a given blade must be shut down when even just one component needs to be replaced.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.